The casement window referred to in the present description usually comprises a rectangular (sometimes a polygonal, arched or the like) framework consisting of a frame anchored within an opening in a wall and a sash swingably mounted thereon with locking means preventing unintended opening of the sash.
IL Patent 115840 to Arpal Aluminum Ltd. describes an adjustable casement window suitable for use as a blast resistant framework illustrated in FIGS. 1 to 3 which are indicated as Prior Art. A rectangular framework 2 for a windowpane 4 is mounted within an opening in a wall 6. The framework comprises an outer frame 8 typically made of steel and anchored within a corresponding rectangular aperture formed in the wall 6 by a portion 11 cast within the wall and by other suitable anchors (not shown), as known per se.
A jamb frame 12 is mounted within the outer frame 8 and consists of an upper frame head 14, a lower frame sill 16, a side shutting jamb 18 and a side hinging jamb 20.
The framework 2 further comprises a window sash 22, which consists of a profiled top rail 24, a bottom rail 26, a shutting stile 28 and a hinging stile 30. The window sash 22 is pivotally mounted with respect to the jamb frame 12 by means of hinges 32, secured respectively to the hinging jamb 20 and the hinging stile 30. The jamb frame 12 and the window sash 22 are typically made of a light metal such as aluminum.
The profiles of the vertical sash members 28 and 30 and the profiles of the horizontal sash members 24 and 26 are respectively formed with inwardly directed pairs of reinforcing flanges 34 and 36 designed to receive the end portion of the window pane 4. These profiles are also provided with suitable seals 38 and 40 for preventing egress or ingress of air, noxious gases, dust and water. The window sash 22 is lockable within the jamb frame 12 by means of a rotary handle 42 mounted on the shutting stile 28 and activating a locking mechanism as known per se.
Locking mechanisms which are in use in the casement windows usually comprise upright (and sometimes also horizontal) sliding carrier members which are activated by a rotary handle and, in turn, displace a number of associated locking elements to bring them into their locked state. A blast-resistant casement window with such a locking system is described, for example, in IL Patent 103168 to Arpal aluminum Ltd., and is effective against distortion and/or detachment with blasts corresponding to one atmosphere pressure (1 Bar=14.2 PSI). Experiments have shown that the above-described frameworks may appear to be ineffective against blasts creating pressures higher than those mentioned above. It has been noticed, that the described air-tight frameworks lose their properties due to bending deformations which appear in vertical and horizontal sash members when blast pressure is momentarily applied to the window pane. Such deformations may cause unlocking of some locking elements, consequent weakening of the lock and sometimes result in collapsing of the window pane into the interior of the shelter or room.